The most common and most likely answer to this crossword clue is the 6 letter word POLYPS
I've seen this crossword clue in Financial Times
P
O
L
Y
P
S
More clues leading to the result POLYPS
- Small growths extremely likely to fill small cracks
- Old cuttlefish, sloppy when dismembered
- Main growths in college and primary school heads
- Many an afterthought for small growths
- Reports about extremely lumpy pedunculated tumours
- Around the beginning of last year, Pops got abnormal growths
- Crop raised by agent going north for the coral reef residents
- Slippery, sloppy sea creatures
Buddy explains!

The straight part
We know that "Main growths" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case main growths = polyps.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does POLYPS mean?
POLYPS noun- An abnormal growth protruding from a mucous membrane
- A cylindrical coelenterate, such as the hydra, having a mouth surrounded with tentacles